Image sensors are semiconductor devices for converting optical images into electrical signals. Two general types of image sensors are charge coupled devices (CCDs) and complementary metal oxide silicon (CMOS) image sensors (CISs). CMOS image sensors are devices for digitizing light using imaging technology. In a unit pixel of a CMOS image sensor, a photo diode and a MOS transistor are formed to sequentially and may detect electrical signals by a switching method to form an image.
A metal-0 layer may be formed under a first metal layer. Metal-0 layer may be used as a local interconnection (LIC) for connecting floating diffusion nodes or connecting a source (e.g. a source follower SF) to a drain of a select transistor Select Tr. The resulting pixel layout generally has a layout structure using a layer having at least metal-2 (e.g. at least three metal layers). However, a stack structure having up to a metal-2 layer (e.g. having at least three metal layers) in a relatively small pixel (e.g. such as a 1.4 μm pixel) may have problems such as sensitivity limitations and/or high processing costs.